The nurse is caring for a male client who reports blood in their stool and has a Hgb 5.6 g/dL (reference range 13.5-18 g/dL), Hct 16.8% (reference range 40-50%), and a WBC 3,400/mm3 (reference range 4500-11,000/mm3). The provider orders 2 units of packed red blood cells (PRBC). While monitoring the patient 10 minutes after starting the blood transfusion, the patient reports a sudden onset of chills, back pain, and appears anxious. What is the nurse's first action?

A. Notify the provider: While notifying the provider is necessary, it is not the first action. Immediate cessation of the transfusion is critical to prevent further exposure to potentially incompatible blood and limit the severity of a transfusion reaction. B. Stop the transfusion immediately: Sudden onset of chills, back pain, and anxiety shortly after starting a blood transfusion are classic signs of an acute hemolytic transfusion reaction, which can be life-threatening. Stopping the transfusion immediately prevents additional hemolysis, reduces the risk of shock, and is the highest-priority intervention to protect the patient. C. Calm and reassure the patient: Reassuring the patient is important for psychological support, but it does not address the acute medical emergency. The priority is to stop the transfusion and prevent further hemolysis or circulatory compromise. D. Check the vital signs: Assessing vital signs is important to determine the severity of the reaction, but the first and most urgent action is to stop the transfusion. Delaying cessation while checking vitals could worsen the patient’s outcome in a potentially fatal transfusion reaction.